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Author Topic: multiple blown horn drivers.  (Read 1437 times)

John Sabine

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multiple blown horn drivers.
« on: December 10, 2012, 08:05:24 am »

For the past month or so I've been using my Yorkville Unity system for my mains because the jobs I've been doing were smaller and also had limited setup/teardown time so my Line Array, including my VTC DLMS 4080, has sat unused. This past weekend I had to pull the line array out again. We only had a total of 3 hours to set up PA, Set up back line, and get a rudimentary sound check done with volume restrictions until showtime. I powered up my system, put on some low level background music and everything sounded fine. We get into the show, which was a rock band, and I notice that the sound is kind of muddy but this is a VERY reverberant room so I'm chalking it up to acoustics. When I walk up front to check my amps I notice that my horns don't seem to be working. I go look at my processor and it has reset itself to default! allowing all pass to every amp.. I've run this processor for 4 years and never had this happen, but yes, I should have looked at the display to make sure that it recalled the proper preset, my fault. Needless to say that I now have 8 blown horn drivers. I reprogram the processor for two way operation and manage to EQ the system to sound at least passable, and manage to limp through the rest of the show. Fortunately I had 4 replacement drivers with me so I was able to get kind of up and going for the next night's job (both jobs last weekend were 120 miles from my shop).
 My line array satellites have a built in 2 way crossover but when you switch from full range to bi-amp the crossovers are removed from the circuit completely. I'm thinking about either reworking the switching network so that the crossover stays in circuit with the horn drivers when the switch is in bi-amp mode or putting a 10uf cap in series with the bi-amp circuit high output so that there is at least some protection for the horns from events such as processor failure or transient thump from amps turning on and off. Since the switch completely takes the crossover out of circuit the additional cap should not interfere with the characteristics of the internal passive crossover during full range operation. Suggestions?
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Ivan Beaver

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Re: multiple blown horn drivers.
« Reply #1 on: December 10, 2012, 02:45:46 pm »

Step one would be to look a the drivers and try to determine exactly what the failure mode is.

THEN you can start to look for possible solutions.

There is no reason to look for a solution to a problem that doesn't exist.

Just throwing a cap in line is NOT the way to go .  You mentioned a 10uf cap.  Is this based on any math?  How did you determine that value.

Don't forget that you will introduce a 90 phase shift with a cap in series, and if the value it not correct it is either affect the freq response or not provide any protection.

My guess is that a 10uf is going to be to small-but I don't know the impedance or freq response of the HF section-so my guess may be completely wrong.

But as of now, we don't know what you need to protect from.
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Ivan Beaver
Danley Sound Labs

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John Sabine

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Re: multiple blown horn drivers.
« Reply #2 on: December 10, 2012, 09:22:12 pm »

Step one would be to look a the drivers and try to determine exactly what the failure mode is.

The failure was caused by my DLMS4080 resetting to default mode and instead of my high range outputs having a hp xover frequency of 2500 hz @ 24db per octave, it sent 2400 watts of full range audio to 8-75 watt titanium horn drivers, causing almost immediate catastrophic failure.

THEN you can start to look for possible solutions.

There is no reason to look for a solution to a problem that doesn't exist.

Just throwing a cap in line is NOT the way to go .  You mentioned a 10uf cap.  Is this based on any math?  How did you determine that value.

Each cab has 2-16 ohm hf drivers in parallel. A 10uf cap at 8 ohms should be 2k with a 6db per octave slope.

Don't forget that you will introduce a 90 phase shift with a cap in series, and if the value it not correct it is either affect the freq response or not provide any protection.

My guess is that a 10uf is going to be to small-but I don't know the impedance or freq response of the HF section-so my guess may be completely wrong.

But as of now, we don't know what you need to protect from.

Another thing I would like to prevent is something that happened to me back in July. I hooked up my rig to check it out before a job and when I turned on the amps one of my highs amps (Yorkville AP1020's that have since been retired) went nuclear and sent DC to all of the horn drivers on one side, smoking them almost instantaneously. I feel that if there had been at least a simple cap in series with the horn drivers there would have at least been some protection.
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Ivan Beaver

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Re: multiple blown horn drivers.
« Reply #3 on: December 11, 2012, 07:14:41 am »

Yes a series cap will protect against DC.  However it needs to of a large enough value (based on impedance of load and low freq response) so that it does not interfere with the freq response.
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Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

John Sabine

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Re: multiple blown horn drivers.
« Reply #4 on: December 11, 2012, 12:58:40 pm »

This is why I had chosen something in the 10uf range. My crossover point in my processor is 2500 @l 24 db/oct so that shouldn't effect it other than the phase shift and some slight attenuation and I can correct for that in the settings on the DLMS 4080


Yes a series cap will protect against DC.  However it needs to of a large enough value (based on impedance of load and low freq response) so that it does not interfere with the freq response.
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Ivan Beaver

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Re: multiple blown horn drivers.
« Reply #5 on: December 11, 2012, 01:03:16 pm »

This is why I had chosen something in the 10uf range. My crossover point in my processor is 2500 @l 24 db/oct so that shouldn't effect it other than the phase shift and some slight attenuation and I can correct for that in the settings on the DLMS 4080
And I will will say for the THIRD TIME  WHAT IS YOUR IMPEDANCE?

That will GREATLY affect the value selected.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

John Sabine

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Re: multiple blown horn drivers.
« Reply #6 on: December 11, 2012, 01:28:23 pm »

This was in my second post:
"Each cab has 2-16 ohm hf drivers in parallel. A 10uf cap at 8 ohms should be 2k with a 6db per octave slope. "




And I will will say for the THIRD TIME  WHAT IS YOUR IMPEDANCE?

That will GREATLY affect the value selected.
« Last Edit: December 11, 2012, 01:34:31 pm by John Sabine »
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dick rees

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Re: multiple blown horn drivers.
« Reply #7 on: December 11, 2012, 01:41:05 pm »

This was in my second post:
"Each cab has 2-16 ohm hf drivers in parallel. A 10uf cap at 8 ohms should be 2k with a 6db per octave slope. "

In Ivan's defense, go and look at your second post.  Proper use of the quote/quote function will bring your answer out so it can be read.  Sorting through a blue block-post is tedious.

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John Sabine

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Re: multiple blown horn drivers.
« Reply #8 on: December 11, 2012, 01:52:23 pm »

Agreed, I can see how he could miss it.

In Ivan's defense, go and look at your second post.  Proper use of the quote/quote function will bring your answer out so it can be read.  Sorting through a blue block-post is tedious.
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Ivan Beaver

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Re: multiple blown horn drivers.
« Reply #9 on: December 11, 2012, 07:04:59 pm »

Agreed, I can see how he could miss it.
Yes-I did not read in the middle of the quoted part.

10uf with 8 ohms would put a 6dB crossover point around 2Khz.

I your electronic crossover is around 2.5Khz, then I would use a higher value cap for a lower crossover point. Say 20uf.

So it does not mess with the existing crossover as much.
 
But that is just me.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!
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